A typical road transportable home, commonly known as a mobile home, is constructed upon a pair of steel longitudinally extending "I" beams which serve as its major structural support members; such "I" beams typically having a 12 inch web and 2 inch upper and lower flanges. The pair of steel longitudinally extending "I" beams typically support a multiplicity of floor joists which extend perpendicularly across the upper flanges of the "I" beams, and which are preferably spaced 16 inches apart along the full length of the mobile home. Such floor joists are typically composed of 2 inch by 8 inch pine stock planks. The house structure of such typical mobile home extends upward from the upper surfaces of its floor joists; the structure being similar to those of common immobile wooden frame houses.
In order to transport a typical mobile home, such as is described above, upon a road, a wheel carriage is temporarily bolted to the steel "I" beams; such wheel carriage typically raising the entire mobile home structure to an elevation wherein the lower flanges of the "I" beams are approximately 16 inches above the road.
Passage of the mobile home beneath bridges often is necessary. The interior height of a typical bridge over a U.S. interstate highway is 16 feet 4 inches. Subtracting the vertical dimensions of the 8 inch floor joists, the 12 inch "I" beams, and the 18 inch road clearance referred to above from a standard 16 foot 4 inch bridge height leaves 13 feet 2 inches as an absolute maximum height of a mobile home house structure which may be erected upon the upper surfaces of its floor joists. In order to be assured of safe clearance when transported beneath interstate bridges, a mobile home is typically constructed so that its structure extends upward from the upper surface of its floor joists no more than 12 feet 7 inches. Such vertical structural space, while being ample for a single story structure, is insufficient for a 2 story split level structure. In the event such 12 foot 7 inch vertical space were utilized for constructing upper and lower split level rooms, a portion of the vertical space would necessarily be dedicated to the vertical dimensions of the roof and of the second floor; leaving less than 6 feet for the interior vertical dimensions of the first and second floor rooms. As a practical matter, an upper floor and a lower floor cannot be situated within a vertical space of 12 feet 7 inches.
A typical mobile home has 4 foot high crawl space beneath its floor joists, such crawl space resulting from mounting of the one foot tall steel "I" beams upon the upper surfaces of piers which typically rise 3 feet above the ground. The instant inventive mobile home utilizes such crawl space by providing a floor section which is alternately downwardly extendable and upwardly retractable; such section allowing, through downward extension, utilization of the vertical dimension of the crawl space as living space, and allowing, through upward retraction, mounting of the mobile home upon a wheel carriage for road transportation.